The present invention relates to a device and method for measuring tire runout, and more specifically to a device and method for accurately measuring tire runout but which is mechanically simple, intuitive to use, yet very accurate.
“Tire runout” describes OD tolerances/variations of a tire relative to its rotational axis when a wheel is rotated on a vehicle. This is important since variations in tire runout result in “humps” on the tire that cause it to shake and vibrate, even after the tire has been balanced. Further, the shake and vibration can be amplified due to harmonic vibrations that come and go at various speeds (depending on how many “humps” are in the tire). Most tires should have less than 0.030 to 0.050 inches of runout. Some trucks and SUVs can tolerate up to 0.060 inch of radial runout. Tire manufacturers set runout specifications, and it is important that small garages and other lower-volume operations be able to accurately measure runout to ensure that the tires they install are within the manufacturer's specification. The devices should be accurate but easy to work with, durable but not overly costly, and relatively simple but effective.
Some measuring devices for measuring tire runout use needle gauges as an indicator. A problem is that in many locations, tire installers are often untrained or not familiar with the needle gauges and thus do not use them correctly (nor take care of them, which can result in poor function). Additionally, the gauges get dirty and/or are difficult to read. For example, the difference between a runout measurement of 0.58 and 0.062 on a runout gauge can be very important, . . . yet it is extremely difficult to tell the difference on most gauges since the gauge's needle indicator moves quickly over a peak of the runout and then quickly drops off as the tire is rotated. Unless the operator takes extra time, the measurement is potentially not accurate, even when an accurate gauge is used. Another problem is that some operators do not have good eyesight, such that they are unable to tell the difference between a narrow range of points on the gauge which, when combined with poor lighting, dirty gauges, and marginal gauge operation, combines to lead to additional inaccurate readings.
Some measuring devices for measuring tire runout are complicated and expensive. For example, see Parker U.S. Pat. No. 6,595,053. While such complicated and expensive devices may be appropriate for sophisticated operations, high-volume operations, and/or OEM assembly plants, they are much too complicated and expensive for most small garage shops and vehicle dealerships.